Russia's Phobos-Grunt space probe, with 22 pounds of radioactive Cobalt-57 on board, fell to Earth Sunday. The probe was launched in November to go to Phobos, a moon of Mars, but its rocket system failed to fire it onward from low Earth orbit.

There is some confusion as to where pieces of the 14.9-ton probe fell. The Associated Press reported Sunday that "pieces" landed in water 1,250 kilometers west of Wellington Island in Chile's south, the Russian military Air and Space Defense Forces said in a statement." The AP dispatch, datelined Moscow, quoted a spokesman, Colonel Alexei Zolotukhin, as saying that this "deserted ocean area is where Russia guides its discarded space cargo ships serving the International Space Station."

But, the article went on: "RIA Novosti news agency, however, cited Russian ballistic experts who said the fragments fell over a broader patch of Earth's surface, spreading from the Atlantic and including the territory of Brazil. It said the midpoint of the crash zone was located in the Brazilian state of Goias."

"The $170 million craft was one of the heaviest and most toxic pieces of space junk ever to crash to Earth, but space officials and experts said the risks posed by its crash were minimal because the toxic rocket fuel on board and most of the craft's structure would burn up in the atmosphere high above the Earth anyway," said the article by Vladimir Isachenkov.

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What happened demonstrates what could have occurred to the plutonium-fueled rover which NASA calls Curiosity which it launched on November 26 on a voyage to Mars. Curiosity's launch went without incident. It is now on its way to Mars. But it could have ended up like Phobos-Grunt--falling back to Earth from orbit, its 10.6 pounds of plutonium released as deadly radioactive dust.

Moreover, the United States and Russia are both planning to launch other space devices with nuclear materials on board. Accidents involving discharge of nuclear materials is inevitable--they've already occurred in both the U.S. and Russian/Soviet space programs.

NASA is not only planning more space missions using plutonium but it is developing nuclear-powered rockets. Some of the rocket designs go back to the 1950s and 60s and the projects had come to an end out of concern of such a rocket blowing up on launch or falling back to Earth. Further, NASA is planning nuclear-powered colonies on the Moon and Mars. These nuclear power systems would be launched from Earth--and there could be release of radioactive material in an accident on launch or a subsequent crash back to Earth.

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Involved is a lethal game of space-borne nuclear Russian roulette.

The Phobos-Grunt space probe "got stranded in Earth's orbit after its Nov. 9 launch," said the AP, "and efforts by Russian and European Space Agency exports to bring it back to life failed." Roscosmos, the Russian space agency, then estimated that Phobos-Grunt would fall to Earth in January and it would come down along a swatch that included southern Europe, the Atlantic, South America and the Pacific.

Roscosmos "predicted that only between 20 and 40 fragments" of the probe "with a total weight of up to 200 kilograms--440 pounds--would survive the re-entry and plummet to Earth," the AP said.

The Cobalt-57 was contained in "one of the craft's instruments," said AP. Roscomos, it said, claimed the Cobalt-57 posed "no threat of radioactive contamination."

Indeed, Cobalt-57 is not plutonium, considered the most deadly radioactive substance. Nevertheless, it still can be harmful.

As the U.S. Department of Energy's Argonne National Laboratory says in a "Human Health Fact Sheet PDF," Cobalt-57 has a half-life of 270 days, "long enough to warrant concern." (The hazardous lifetime of a radioactive material is 10 to 20 times its half-life.) The "Human Health Fact Sheets" notes that Cobalt-57 can cause cancer. It "can be taken into the body by eating food, drinking water, or breathing."

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The AP article Sunday said the $170 million Phobos-Grunt involved " Russia's most expensive and most ambitious space mission since Soviet times." The last Soviet interplanetary mission occurred in 1996: a probe to go to Mars "built by the same Moscow-based NPO Lavochkin company" which constructed Phobos-Grunt, said AP. The Mars 96 space probe had plutonium on board.

It also "experienced an engine failure and crashed shortly after its launch," said AP. The Mars 96 space probe "crash drew strong international fears because of around 200 grams of plutonium on board. The craft eventually showered its fragments over the Chile-Bolivia border in the Andes Mountains, and the pieces were never recovered."

The AP article said the "worst ever radiation spill from a derelict space vehicle," the crash back to Earth in 1978 of the Cosmos 954 satellite that contained a working nuclear reactor. Radioactive debris fell over northwestern Canada.